Flat-panel display devices are widely used in conjunction with computing devices, in portable devices, and for entertainment devices such as televisions. Such displays typically employ a plurality of pixels distributed over a substrate to display images. The substrate is typically a continuous sheet of glass, but can be plastic or other materials, and can be divided into multiple adjacent tiles. Each pixel incorporates several, differently colored light-emitting elements commonly referred to as sub-pixels, typically emitting red, green, and blue light, to represent each image element. As used herein, pixels and sub-pixels are not distinguished and refer to a single light-emitting element. A variety of flat-panel display technologies are known, for example plasma displays, liquid crystal displays, and electroluminescent (EL) displays, such as light-emitting diode (LED) displays.
EL displays incorporating thin films of light-emitting materials forming light-emitting elements have many advantages in a flat-panel display device and are useful in optical systems. U.S. Pat. No. 6,384,529 to Tang et al. shows an organic light-emitting diode (OLED) color display that includes an array of organic LED light-emitting elements. Alternatively, inorganic materials can be employed and can include phosphorescent crystals or quantum dots in a polycrystalline semiconductor matrix. Other thin films of organic or inorganic materials known in the art can also be employed to control charge injection, transport, or blocking to the light-emitting-thin-film materials. The materials are placed upon a substrate between electrodes, with an encapsulating cover layer or plate. Light is emitted from a pixel when current passes through the light-emitting material. The frequency of the emitted light is dependent on the nature of the material used. In such a display, light can be emitted through the substrate (a bottom emitter) or through the encapsulating cover (a top emitter), or both.
Control of sub-pixels is typically accomplished with row electrodes and orthogonal column electrodes, in an active- or passive-matrix configuration as known in the art. However, these configurations limit the timing flexibility of the display. Furthermore, in active-matrix displays, each subpixel includes one or more thin-film transistors (TFTs), and such transistors have undesirable nonuniformity (e.g. low-temperature polysilicon, LTPS, TFTs) or aging (e.g. amorphous silicon, a-Si, TFTs).
Employing an alternative control technique, Matsumura et al. describe crystalline silicon substrates used for driving LCD displays in U.S. Patent Application Publication No. 2006/0055864. The application describes a method for selectively transferring and affixing pixel-control devices (“chiplets”) made from semiconductor substrates onto a separate planar display substrate. Wiring interconnections within the pixel-control device and connections from busses and control electrodes to the pixel-control device are shown. A matrix-addressing pixel control technique is taught.
The technique of Matsumura overcomes the TFT limitations of the prior art. However, in high-resolution or high-frame-rate displays, this technique is limited by the electrical properties of the row and column electrodes used to transmit pixel information, information controlling the subpixels, to the chiplets. These electrodes have crosstalk and resistive, inductive and capacitive delays that are very difficult to overcome.
In other fields, it is known to overcome limitations of electrical signaling using optical signaling. For example, U.S. Pat. No. 5,726,786 to Heflinger teaches a free-space optical interconnect (FSOI) in which transceivers send and receive information using light propagating through a transmission volume such as an integrating chamber. U.S. Patent Application Publication No. 2008/0008472 to Dress et al. teaches an optical broadcast interconnect using one lens per transmitter and one lens per receiver to permit a transmitter to efficiently transmit light simultaneously to many receivers. These two applications permit effective optical communication e.g. from a controller to many receivers, but only in a large optical volume. These schemes are not, therefore, suitable for flat-panel displays, which have significant constraints on space and particularly on thickness.
U.S. Pat. No. 6,141,465 to Bischel et al. teaches a display device using optical waveguides and poled electro-optical structures to direct light from the edge of a flat display out to a viewer. This scheme permits light to be transmitted through the substrate of a display and extracted at a desired point. However, the poled electro-optical structures are complex and require expensive manufacturing processes. Furthermore, this scheme is directed to a light output for pixels, a very different problem than control-signal distribution for chiplets.
U.S. Pat. No. 6,259,838 to Singh et al. teaches a display device employing a plurality of light-emitting elements disposed along the length of a light-emitting fiber, such as an optical fiber. This scheme provides optical control of OLED display elements. However, in high-resolution displays, this scheme requires precise positioning of a large number of fibers, e.g. one per row. Positioning errors can cause visible non-uniformity and reduce yields. Furthermore, any breaks in the fiber can deactivate all pixels after the break, or all pixels attached to that fiber.
There is a need, therefore, for improving the distribution of pixel control information to chiplets on a display device.